simplify

learned tricks from mozilla#306

rust-overlay.nix

@@ -290,22 +290,18 @@ let
                   cp --remove-destination "$(realpath -e $target)" $target
                 fi
 
-                # The SYSROOT is determined by using the librustc_driver-*.so.
+                # The SYSROOT is determined by using the librustc_driver-*.{so,dylib}.
                 # So, we need to point to the *.so files in our derivation.
                 if ls $out/lib/*.so &>/dev/null; then
                   chmod u+w $target
                   patchelf --set-rpath "$out/lib" $target || true
                 fi
               done
 
-              # Here we copy the librustc_driver-*.{so|dylib} to our derivation.
+              # Here we copy the librustc_driver-*.{so,dylib} to our derivation.
               # The SYSROOT is determined based on the path of this library.
-              if ls $out/lib/librustc_driver-*.so &>/dev/null; then
-                RUSTC_DRIVER_PATH=$(realpath -e $out/lib/librustc_driver-*.so)
-                cp --remove-destination $RUSTC_DRIVER_PATH $out/lib/
-              fi
-              if ls $out/lib/librustc_driver-*.dylib &>/dev/null; then
-                RUSTC_DRIVER_PATH=$(realpath -e $out/lib/librustc_driver-*.dylib)
+              if ls $out/lib/librustc_driver-*.{so,dylib} &>/dev/null; then
+                RUSTC_DRIVER_PATH=$(realpath -e $out/lib/librustc_driver-*.{so,dylib})
                 cp --remove-destination $RUSTC_DRIVER_PATH $out/lib/
               fi
             '';